/*
 *      idt.c
 *
 *      Copyright 2007 Giulio Bai <giulio@hewle.com>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA
 */

#include <io2.h>
#include <idt.h>

/* Defines an IDT entry */
struct idt_entry
{
	unsigned short base_lo;
	unsigned short sel;        /* Our kernel segment goes here! */
	unsigned char always0;     /* This will ALWAYS be set to 0! */
	unsigned char flags;       /* Set using the above table! */
	unsigned short base_hi;
} __attribute__((packed));


struct idt_ptr
{
	unsigned short limit;
	unsigned int base;
} __attribute__((packed));


/* Declare an IDT of 256 entries. Although we will only use the
 *  first 32 entries, the rest exists as a bit of a trap.
 * If any undefined IDT entry is hit, it normally
 *  will cause an "Unhandled Interrupt" exception. Any descriptor
 *  for which the 'presence' bit is cleared (0) will generate an
 *  "Unhandled Interrupt" exception */
struct idt_entry idt[256];
struct idt_ptr   idtp;

/* This exists in 'start.asm', and is used to load our IDT */
extern void _idt_load ();

/* Use this function to set an entry in the IDT. Alot simpler
 *  than twiddling with the GDT ;) */
void idt_set_gate (unsigned char num, unsigned long base, unsigned short sel, unsigned char flags)
{
	/* Split base into low and high 16-bit parts */
	idt[num].base_lo = (base & 0xFFFF);
	idt[num].base_hi = (base >> 16) & 0xFFFF;
	
	idt[num].sel     = sel;
	idt[num].always0 = 0; /* Always set to 0! */
	idt[num].flags   = flags;
}

/* Installs the IDT */
void idt_install (void)
{
    /* Sets the special IDT pointer up, just like in 'gdt.c' */
    idtp.limit = (sizeof (struct idt_entry) * 256) - 1;
    idtp.base  = &idt;

    /* Clear out the entire IDT, initializing it to zeros */
    memset (&idt, 0, sizeof (struct idt_entry) * 256);

    /* Add any new ISRs to the IDT here using idt_set_gate */

    /* Points the processor's internal register to the new IDT */
    _idt_load ();
    
    printi ("interrupt descriptor table", 4, 1);
}
